Sir Terry Pratchett has died at the age of 66 after a long battle with Alzheimer's disease.
His publishers, Penguin, confirmed the sad news in a tweet this afternoon.
His good friend Rob Wilkins, who co-ran Terry's Twitter account with him, also tweeted in a very Pratchett-like way.
Terry's colleague Larry Finlay, the managing director at Transworld Publishers, said he was "deeply saddened" by the news, and called him one of the world's "brightest, sharpest minds".
"In over 70 books, Terry enriched the planet like few before him. As all who read him know, Discworld was his vehicle to satirize this world: he did so brilliantly, with great skill, enormous humour and constant invention," he continued.
"Terry faced his Alzheimer's disease (an 'embuggerance', as he called it) publicly and bravely. Over the last few years, it was his writing that sustained him. His legacy will endure for decades to come."
The author - who was a vocal campaigner for euthanasia - died at home surrounded by his family "with his cat sleeping on his bed", Larry's statement added.
Terry was diagnosed with the progressive disease in 2007, but was determined to continue writing until he no longer could.
He finished his last book, a Discworld sequel, last summer.
A JustGiving page has been set up in Sir Terry's memory, with all the proceeds going towards the Research Institute for the Care of Older People (RICE). More than £2,000 has already been raised.